1. Field of the Invention
This invention relates to a photo-electric converter to be adopted in a light information input device which is one of the constituent elements of an image forming apparatus, etc. to form an image by actuating a recording head (e.g. an ink jet head) constructed with a plurality of writing elements using image signals obtained by two-dimensional scanning of documents, papers, and other image originals.
2. Description of the Prior Arts
Remarkable development and progress have been attained recently in the field of the image forming apparatus such as a reproduction or duplicating apparatus, and so forth. Yet, there still remains various problems to be solved such as the increase in density densification in reading and writing of image information from and into the image forming apparatus, speed increase in such reading and writing operations, simplification of the signal processing system in the apparatus, and others. Take the increase in density in writing for example. The most general way of writing in such image forming apparatus has been to arrange a plurality of writing elements in one row or rank, and to move an array of the writing elements (recording head) in a direction orthogonal to the row of the writing elements, thereby performing the two-dimensional scanning. This way of writing, however, is difficult to implement when the spacing between the writing elements is greater than a desired pitch of writing picture element (pel). Even if an ink jet head is taken as an example of the recording head, the minimum spacing of discharge orifices of the ink jet head array is of an order of 0.25 mm or so, and hence a value of 4 pel/mm or so becomes the maximum recording pel density. With this writing density, however, the image resolution will fall short of the recording images of documents and papers in general, for which a pel density of at least 12 pel/mm is desired. Further, in accordance with the pel density, there arises the necessity for a reading apparatus capable of reading high density pel signals.
One way of attaining such purposes has been disclosed in a Japanese patent Laid-Open Publication No. 53-136835 (corresponding to U.S. Pat. No. 4,112,469). In this published application, the printer reads a document with a high density by an interlace system using a one-dimensional photo-sensor array with n photo-diodes being arranged at a certain definite spacing, and performs high density recording in the same interlace system as the read-scanning using a print head constructed by arranging n nozzles with a certain definite spacing. Incidentally, for the entire document having a two-dimensional plane to be scanned with the one-dimensional photo-sensor array, it becomes necessary to provide a scanning optical system for moving a photo-sensor array image over the document in the direction perpendicular to the length of the array and along at least the width of the document. As will be readily understood, in the high speed recording a scanning optical system of very high scanning speed is demanded, which is not favorable from the technical standpoint. Accordingly, now that the technique in the two-dimensional photo-sensor array has been developed, it is desirable to remedy the above-mentioned defect by performing the read-scanning with use of the two-dimensional photo-sensor array. Accordingly, the following two main points should be taken into consideration as to the technique required.
The first point is to obtain a reading system which uses the two-dimensional photo-sensor array, and is capable of reading pel signals with a reading density in conformity with a desired writing density. Generally speaking, since the number of the reading pels accomplishing a desired writing density is far more than the number of the photo-sensor elements constituting the two-dimensional photo-sensor array, and since the photo-sensor element pitch cannot be made as small as the pitch of the pels, it becomes necessary to provide a device for reading the entire pels on the surface of the image original, while inserting an appropriate pitch therebetween. The method of insertion should further be convenient for the writing system. For instance, when the writing system of the printer as disclosed in the aforementioned Japanese patent Laid-Open Publication No. 53-136835 (corresponding to U.S. Pat. No. 4,112,469) is to be employed, it becomes necessary to provide a signal processing system which once stores therein pel signals to be obtained from the two-dimensional photo-sensor array, and then rearranges the pel signals for the interlace writing.
The second point is therefore to provide a device which adopts the image reading and writing system capable of simplifying the signal processing system.